On 10/29/2012 7:14 AM, W5DXP wrote:
On Sunday, October 28, 2012 6:18:58 PM UTC-5, Channel Jumper wrote:
But your dipole antenna needs to be resonant - 1/2 wavelength on the
lowest frequency you desire to operate on.

Like the G5RV that you dislike, if one removed the feedline from a 1/2WL resonant center-fed dipole, it is no longer resonant. Resonance implies a low resistive feedpoint impedance. The G5RV antenna system has a low resistive impedance looking into the series matching section on 75m, 40m, and 20m (also on 12m).

3/2WL dipole + 1/2WL feedline = resonance on 20m

3/4WL dipole + 1/4WL feedline = resonance on 40m

3/8WL dipole + 1/8WL feedline = resonance on 75m.

The (G5RV) ladder line is the matching network and it only works on 20 meters.

Here's technical proof that it also works on 75m and 40m.

http://www.w5dxp.com/G5RV.HTM

The Smith Chart SWR arc indicates how series section transformers really work. The G5RV is a reasonably good antenna on 75m, 40m, 20m, and 12m. Not so good on 15m and not good at all on 30m, 17m, and 10m. A ZS6BKW is a better choice to obtain 17m and 10m but one loses 75m.

The G5RV antenna system is what it is. It is neither a gift from Heaven nor a design straight from Hell.
--
73, Cecil, w5dxp.com


Unfortunately that is not proof. Proof is when you compare a tuned
dipole on say 75 and a 102 foot G5RV side by side with a switch to a
simple 1/2 wave dipole. Actual testing like this is required.
Mathematics and graphs are simply that, mathematics and graphs. Those
little plots assume that there are no other variables that have not been
considered or even discovered.

Every time I hear a poor signal breaking into our conversation on 75,
and I ask what is their antenna? You guessed it, a G5RV. I always ask
during any qso what antenna they are using and at what power.

No, it is not a design from hell. It is just a poor excuse for a
multi-band antenna. A trapped multi-band dipole will work better from my
experience and I don't like trapped multi-band antennas. The only
antennas that sound weaker on 75 than the G5RV are the random wire
antennas and a vertical using about 4 or 5 buried ground radials. So,
the G5RV is a step up from those horrible antennas.

The G5RV is only gotten popular because it is cheap to buy and easy to
erect. Performance is very difficult for most ham operators to ascertain
because they have nothing with which to compare their G5RV. Many hams
will give someone who is weak a 5/9 reading just to be congenial. They
are not doing the other operators any favours doing this. I always give
my peak s meter readings. This is certainly not a great standard, but is
honest on my part.

So, Cecil, I think you need to erect a simple 75 meter dipole and a coax
switch. See what the other guys says about your two different s meter
readings on 75 meters. This must be done at different time of the day
and night a often. Keep a log of the results.

Michael